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• From where does the game engines add location of an object?

  - by Player

  I have started making my first game( a pong game )with ruby (Gosu). I'm trying to detect the collision of two images using their location by comparing the location of the object (a ball) to another one(a player). For example: if (@player.x - @ball.x).abs <=184 && (@player.y - @ball.y).abs <= 40 @ball.vx = [email protected] @ball.vy = [email protected] But my problem is that with these numbers, the ball collides near the player sometimes, even though the dimensions of the player are correct. So my question is from where does the x values start to count? Is it from the center of gravity of the image or from the beginning of the image? (i.e When you add the image on a specific x,y,z what are these values compared to the image?

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• Can't detect collision properly using Rectangle.Intersects()

  - by Daniel Ribeiro

  I'm using a single sprite sheet image as the main texture for my breakout game. The image is this: My code is a little confusing, since I'm creating two elements from the same Texture using a Point, to represent the element size and its position on the sheet, a Vector, to represent its position on the viewport and a Rectangle that represents the element itself. Texture2D sheet; Point paddleSize = new Point(112, 24); Point paddleSheetPosition = new Point(0, 240); Vector2 paddleViewportPosition; Rectangle paddleRectangle; Point ballSize = new Point(24, 24); Point ballSheetPosition = new Point(160, 240); Vector2 ballViewportPosition; Rectangle ballRectangle; Vector2 ballVelocity; My initialization is a little confusing as well, but it works as expected: paddleViewportPosition = new Vector2((GraphicsDevice.Viewport.Bounds.Width - paddleSize.X) / 2, GraphicsDevice.Viewport.Bounds.Height - (paddleSize.Y * 2)); paddleRectangle = new Rectangle(paddleSheetPosition.X, paddleSheetPosition.Y, paddleSize.X, paddleSize.Y); Random random = new Random(); ballViewportPosition = new Vector2(random.Next(GraphicsDevice.Viewport.Bounds.Width), random.Next(GraphicsDevice.Viewport.Bounds.Top, GraphicsDevice.Viewport.Bounds.Height / 2)); ballRectangle = new Rectangle(ballSheetPosition.X, ballSheetPosition.Y, ballSize.X, ballSize.Y); ballVelocity = new Vector2(3f, 3f); The problem is I can't detect the collision properly, using this code: if(ballRectangle.Intersects(paddleRectangle)) { ballVelocity.Y = -ballVelocity.Y; } What am I doing wrong?

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• Box 2D Collision Question

  - by Farooq Arshed

  I am very new to Box 2D Physics world. I wanted to know how to collide 2 bodies when one is Dynamic and other is Kinematic. The whole Scenario is explained below: I have 3 balls in total. I want to balls to remain in their places and the third ball to be able to move. When the third ball hits the other two balls then they should move according to the speed and direction from which they were hit. My gravity of the world is 0 because I only want z-axis gravity. I would also like some one to point me towards some good tutorials regarding Box 2D basics which is language independent. I hope I have explained my scenario well. Thanks for the help in advance.

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• Collision planes confusion

  - by Jeffrey

  I'm following this tutorial by thecplusplusguy and in the linked video he explain that for example for the world basement and walls we need to create the actual rendered (shown to the player) walls and then duplicate them, place them in the same coordinates as the rendered walls and call them collision (by defining their material to collision). Then it defines in the Object loader function that those objects with material == collision are collision planes and should not be rendered but just used to check collision. Now I'm pretty confused. Why would we add this kind of complexity to a problem that can easily be solved by a simple loadObject(string plane_object, bool check_collision);: Creating only the walls object (by loading .obj file in plane_object) Define them also as collision planes whenever the check_collision is set to true In this case we have lowered the complexity of his method and make it more flexible and faster to develop (faster because we don't always have to make a copy for each plane and flexible because we don't hardcode the Object loader). The only case in which this method could not work is when we need hidden collision planes, and for that we could modify the loadObject() function like this: loadObject(string plane_object, bool check_collision = true, bool hide_object = false); Creating only the walls object (by loading .obj file in plane_object) Define them also as collision planes whenever the check_collision is set to true And add the ability to actually show the object or hide it based on hide_object. The final question is: am I right? What would the possible problem encountered with my solution versus his?

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• How does a collision engine work?

  - by JXPheonix

  Original question: Click me How exactly does a collision engine work? This is an extremely broad question. What code keeps things bouncing against each other, what code makes the player walk into a wall instead of walk through the wall? How does the code constantly refresh the players position and objects position to keep gravity and collision working as it should? If you don't know what a collision engine is, basically it's generally used in platform games to make the player acutally hit walls and the like. There's the 2D type and the 3D type, but they all accomplish the same thing: collision. So, what keeps a collision engine ticking?

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• Debugging Minimum Translation Vector

  - by SyntheCypher

  I implemented the minimum translation vector from codezealot's tutorial on SAT (Separating Axis Theorem) but I'm having an issue I can't quite figure out. Here's the example I have: As you can see in top and bottom left images regardless of the side the of the green car which red car is penetrating the MTV for the red car still remains as a negative number also here is the same example when the front of the red car is facing the opposite direction the number will always be positive. When the red car is past the half way through the green car it should switch polarity. I thought I'd compensated for this in my code, but apparently not either that or it's a bug I can find. Here is my function for finding and returning the MTV, any help would be much appreciated: Code

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• Get collision details from Rectangle.Intersects()

  - by Daniel Ribeiro

  I have a Breakout game in which, at some point, I detect the collision between the ball and the paddle with something like this: // Ball class rectangle.Intersects(paddle.Rectangle); Is there any way I can get the exact coordinates of the collision, or any details about it, with the current XNA API? I thought of doing some basic calculations, such as comparing the exact coordinates of each object on the moment of the collision. It would look something like this: // Ball class if((rectangle.X - paddle.Rectangle.X) < (paddle.Rectangle.Width / 2)) // Collision happened on the left side else // Collision happened on the right side But I'm not sure this is the correct way to do it. Do you guys have any tips on maybe an engine I might have to use to achieve that? Or even good coding practices using this method?

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• What has the most efficient intersection test against an AABB tree - OBB, Cylinder or Capsule?

  - by identitycrisisuk

  I'm currently trying to find collisions in 3D between a tighter volume than an AABB and a tree of AABB volumes. I just need to know whether they are intersecting, no closest distance or collision response. An OBB, Cylinder or Capsule would all roughly fit these purposes but Cylinder and Capsule were the first thing I thought of, which I have found little information about detecting intersections online. Am I right in thinking that they would always be more complex to perform Separating Axis Tests on even though they might seem like simpler shapes? I figure by the time I get my head around SAT for curved shapes I could have done the thing with OBBs but I wanted to find out for sure.

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• Big level objects collision system for 2d game

  - by Aristarhys

  I read many variants today and get some knowledge in general, so here is a steps of mine thoughts in pictures (horrible paint.net ones). We need to develop grid system, so we check only thing near, perform simple check to cut out deep check, and at - last deep check like per-pixel collision check. Step 1 - Let p1, p2 are some sprites lets first just check with circle collision - because large distance between p1, p2 this fails and of course so we don't need test more deeply. But if we have not 2, but 20 objects, why we need to even circle test something so far outside of our view. Step 2 - Add basic column system, now we don't bother with p2 if it's in a column far from p1 column, so we even don't do circle test. But p3 is in the same col, so let do circle test, which of course will fail. Step 3 - Lets improve column system to the grid system with grid cell size just like p1, p2, p3 collision boxes, so we cut out things much top or below p1. And this is all great until comes BIG OBJs which is some kind of platforms. They are much bigger then grid cell. Circle test for will be successful, but deep check for whole big obj will fail And that the part I can't get. How do I store the grid position of big object? Like 4 grid coords for big object vertexes? And if one of them close to p1 do circle check for centre of big object then a deep one if succeed? Am I do it wrong? My possible solution:

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• Calculate the intersection depth between a rectangle and a right triangle

  - by Celarix

  all. I'm working on a 2D platformer built in C#/XNA, and I'm having a lot of problems calculating the intersection depth between a standard rectangle (used for sprites) and a right triangle (used for sloping tiles). Ideally, the rectangle will collide with the solid edges of the triangle, and its bottom-center point will collide with the sloped edge. I've been fighting with this for a couple of days now, and I can't make sense of it. So far, the method detects intersections (somewhat), but it reports wildly wrong depths. How does one properly calculate the depth? Is there something I'm missing? Thanks!

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• Collision checking problem on a Tiled map

  - by nosferat

  I'm working on a pacman styled dungeon crawler, using the free oryx sprites. I've created the map using Tiled, separating the floor, walls and treasure in three different layers. After importing the map in libGDX, it renders fine. I also added the player character, for now it just moves into one direction, the player cannot control it yet. I wanted to add collision and I was planning to do this by checking if the player's new position is on a wall tile. Therefore as you can see in the following code snippet, I get the tile type of the appropriate tile and if it is not zero (since on that layer there is nothing except the wall tile) it is a collision and the player cannot move further: final Vector2 newPos = charController.move(warrior.getX(), warrior.getY()); if(!collided(newPos)) { warrior.setPosition(newPos.x, newPos.y); warrior.flip(charController.flipX(), charController.flipY()); } [..] private boolean collided(Vector2 newPos) { int row = (int) Math.floor((newPos.x / 32)); int col = (int) Math.floor((newPos.y / 32)); int tileType = tiledMap.layers.get(1).tiles[row][col]; if (tileType == 0) { return false; } return true; } The character only moves one tile with this code: If I reduce the col value by two it two more tiles. I think the problem will be around indexing, but I'm totally confused because the zero in the coordinate system of libGDX is in the bottom left corner of the screen, and I don't know the tiles array's indexing is similair or not. The size of the map is 19x21 tiles and looks like the following (the starting position of the player is marked with blue:

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• Almost working 2D Collisions

  - by TheGag96

  I'm terribly sorry I'm asking this question YET AGAIN, but I can almost guarantee that this will be the last time I'll have to ask. I'm currently on the verge of FINALLY getting these collisions to work for my game, made with libGDX in Java. My collisions use the same method as (and are basically copied and modified code from) the XNA Platformer example (here) where the direction of the collision is based on the rectangle where two objects are overlapping. The collisions themselves almost work perfectly, but for some reason, holding down/up and left and colliding with the floor/ceiling while doing so doesn't seem to work well. I'm not at all sure why. Instead of vaguely giving my problem and snippets of code, I've decided to instead provide a binary and the source of the game I have so far so you can see for yourself what my problem is. Link. (Note: make sure you unzip everything into a folder somewhere or it will not work) You'll find the collision code in the method workingCollisions() in Link.java. Please excuse the messy code and terrible graphics as this whole thing is in pre-pre-alpha. If anyone is kind enough and helps me out here, you are the best person ever. I'm completely desperate; I've been trying this on and off for months and I just can't get it to work. I cannot thank you enough.

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• AABB - AABB Collision, which face do I hit?

  - by PeeS

  To allow my objects to slide when they collide, I need to : Know which face of the AABB they collide with. Calculate the normal to that face. Return the normal and calculate the impulse that to apply to the player's velocity. Question How can I calculate which face of the AABB I collided with, knowing that I have two AABB's colliding? One is the player and the other is a world object. Here's what that looks like (problem collision circled in white): Thank you for your help.

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• Vector.Unproject - Checking if a model intersects a large sprite

  - by Fibericon

  Let's say I have a sprite, drawn like this: spriteBatch.Draw(levelCannons[i].texture, levelCannons[i].position, null, alpha, levelCannons[i].rotation, Vector2.Zero, scale, SpriteEffects.None, 0); Picture levelCannon as being a laser beam that goes across the entire screen. I need to see if my 3d model intersects with the screen space inhabited by the sprite. I managed to dig up Vector.Unproject, but that seems to only be useful when dealing with a single point in 2d space, rather than an area. What can I do in my case?

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• this.BoundingBox.Intersects(Wall[0].BoundingBox) not working properly

  - by Pieter

  I seem to be having this problem a lot, I'm still learning XNA / C# and well, trying to make a classic paddle and ball game. The problem I run into (and after debugging have no answer) is that everytime I run my game and press either of the movement keys, the Paddle won't move. Debugging shows that it never gets to the movement part, but I can't understand why not? Here's my code: // This is the If statement for checking Left movement. if (keyboardState.IsKeyDown(Keys.Left) || keyboardState.IsKeyDown(Keys.A)) { if (!CheckCollision(walls[0])) { Location.X -= Velocity; } } //This is the CheckCollision(Wall wall) boolean public bool CheckCollision(Wall wall) { if (this.BoundingBox.Intersects(wall.BoundingBox)) { return true; } return false; } As far as I can tell there should be absolutely no problem with this, I initialize the bounding box in the constructor whenever a new instance of Walls and Paddle is created. this.BoundingBox = new Rectangle(0, 0, Sprite.Width, Sprite.Height); Any idea as to why this isn't working? I have previously succeeded with using the whole Location.X < Wall.Location.X + Wall.Texture.Width code... But to me that seems like too much coding if a simple boolean check could be done.

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• Tiled Editor: How is this Map Handling Collision?

  - by user2736286

  BrowserQuest map in question. From what I understand, with tiled, there are two main ways to specify collision: Create an object layer, and interpret the shapes in the engine as collision objects. Create a tiled layer, and make all tiles in the layer have a collision property, and interpret all tiles in the layer as collision objects. I'm using BrowserQuest as a big source of inspiration for my project, and I want to know how they handled collision on the level editing side. I've checked through all their layers, expecting an object layer to be handling cliff collision like: But there are no such object layers to be found. Furthermore, the tile layers containing the tiles for such cliffs have no properties at all, meaning that they didn't just specify "collision" for such tile layers. I especially need to know how they handled less rectangular shapes like: I could imagine that they are not using explicit collision layers, but instead determining collision in the actual engine, based off the presence of specific tile layer sprites. Only because BrowserQuest has whole-tile movement, and it wouldn't look too odd if a small apple, taking up only a fraction of the tile size, prevents movement over that entire tile. But I'm creating a game with more precise movement, so collision has to be tight to the apple, and I really want to know how BrowserQuest approached collision defining. If anyone knowledgeable with Tiled could take a quick look at the map, I'd appreciate it! I'm tearing my hair out here :). Thanks

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• How to make an object move again after being stopped by collision in Unity?

  - by Matthew Underwood

  I have a player object which position is always centered on the main camera's viewport. This object has a Rigidbody 2D, a box and circle collider. The player moves around a level, the level has a polygon collider attached. I move the camera until the object hits against the collider, which stops the movement of the camera by setting its speed to 0. The problem happens when I want to move the camera / player object away from the collider. As the speed is already at 0, it cannot move away from the collider. The script attached to the player object, checks for collisions and applies the speed to 0 on the main camera's test script. using UnityEngine; using System.Collections; public class move : MonoBehaviour { public float speed; public test testing; // Use this for initialization void Start () { speed = 10F; testing = Camera.main.GetComponent<test>(); } // Update is called once per frame void FixedUpdate () { Vector3 p = Camera.main.ViewportToWorldPoint(new Vector3(0.5F, 0.5F, Camera.main.nearClipPlane)); transform.position = new Vector3(p.x, p.y, -1); } void OnCollisionEnter2D(Collision2D col) { testing.speed = 0; } void OnCollisionExit2D(Collision2D col) { testing.speed = 10F; } } This is the script attached to the main camera; just a simple script that changes the camera's position. using UnityEngine; using System.Collections; public class test : MonoBehaviour { public float speed; public float translationY; public float translationX; // Use this for initialization void Start () { speed = 10F; } void FixedUpdate () { translationY = Input.GetAxis("Vertical") * speed * Time.deltaTime; translationX = Input.GetAxis("Horizontal") * speed * Time.deltaTime; transform.Translate(translationX, translationY, 0); } } The player object isn't kinematic and is a fixed angle, the colliders aren't triggers and the polygon collider isn't a trigger either. The player is the red square, the collider is the pink area. -- EDIT -- From the latest change the collider set up for the player So if the X speed was disabled. It wouldnt move into the side of the polygon colider which is good, but yet you couldnt move away from it. And moving down would move inside the colider.

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• Unity Problem with colliding instances of same object

  - by Kuba Sienkiewicz

  I want to check if object's instance is overlapping with another instance (any spawned object with another spawned object, not necessary the same object). I'm doing this by detecting collisions between bodies. But I have a problem. Spawned object (instances) are detecting collision with everything but other spawned objects. I've checked collision layers etc. All of spawned objects have rigidbodies and mesh colliders. Also when I attach my script to another body and I touch that body with an instanced object it detects collision. So problem is visible only in collision between spawned objects. And one more information I have script, rigid body and collider attached to child of main object. using UnityEngine; using System.Collections; public class CantPlace : MonoBehaviour { public bool collided = false; // Use this for initialization void Start () { } // Update is called once per frame void Update () { //Debug.Log (collided); } void OnTriggerEnter(Collider collider) { //if (true) { //foreach (Transform child in this.transform) { // if (child.name == "Cylinder") { //collided = true; Color c; c = this.renderer.material.color; c.g = 0f; c.b = 1f; c.r = 0f; this.renderer.material.color = c; Debug.Log (collider.name); //} // } //} //foreach (ContactPoint contact in collision.contacts) { // Debug.DrawRay(contact.point, contact.normal, Color.red,15f); // } } }

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• Sensor based vs. AABB based collision

  - by Hillel

  I'm trying to write a simple collision system, which will probably be primarily used for 2D platformers, and I've been planning out an AABB system for a few weeks now, which will work seamlessly with my grid data structure optimization. I picked AABB because I want a simple system, but I also want it to be perfect. Now, I've been hearing a lot lately about a different method to handle collision, using sensors, which are placed in the important parts of the entity. I understand it's a good way to handle slopes, better than AABB collision. The thing is, I can't find a basic explanation of how it works, let alone a comparison of it and the AABB method. If someone could explain it to me, or point me to a good tutorial, I'd very much appreciate it, and also a comparison of the advantages and disadvantages of the two techniques would be nice.

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• Trying to create a sphere in UDK on which I can stand

  - by Dave

  Trying to build a globe in UDK, but when I do (create a sphere), my player falls straight through it. How do I make a sphere that I can walk on? Every other shape (cube, cone...etc) work just fine. -- Edit: Specifically, I want to build a CSG/Brush sphere, not a mesh sphere. It appears to work just fine if I set the "sphere exptrapolation" to 1 or 2, but if I bump it up to 3 or higher, I fall right through. I literally created 2 spheres next to each other, one set at "2" and one at "3" - I can walk from the top of the "2" sphere and jump onto the "3" sphere, but I fall right through it.

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• How to detect collisions between sprite and a user generated shape of some sort?

  - by Huwell

  How to detect a collision between a sprite and a user generated shape of some sort. For example. There are some objects on the screen. The user takes their finger and draws an circle shape around a object (The selection rule is painting circle around the sprite, but the painting shapes may be various). I need to detect which object selected, which just like: (demo images) http://i52.tinypic.com/28h0t1g.png

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• Better way to go up/down slope based on yaw?

  - by CyanPrime

  Alright, so I got a bit of movement code and I'm thinking I'm going to need to manually input when to go up/down a slope. All I got to work with is the slope's normal, and vector, and My current and previous position, and my yaw. Is there a better way to rotate whether I go up or down the slope based on my yaw? Vector3f move = new Vector3f(0,0,0); move.x = (float)-Math.toDegrees(Math.cos(Math.toRadians(yaw))); move.z = (float)-Math.toDegrees(Math.sin(Math.toRadians(yaw))); move.normalise(); if(move.z < 0 && slopeNormal.z > 0 || move.z > 0 && slopeNormal.z < 0){ if(move.x < 0 && slopeNormal.x > 0 || move.x > 0 && slopeNormal.x < 0){ move.y += slopeVec.y; } } if(move.z > 0 && slopeNormal.z > 0 || move.z < 0 && slopeNormal.z < 0){ if(move.x > 0 && slopeNormal.x > 0 || move.x < 0 && slopeNormal.x < 0){ move.y -= slopeVec.y; } } move.scale(movementSpeed * delta); Vector3f.add(pos, move, pos);

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• Collision with half of a semi-circle

  - by heitortsergent

  I am trying to port a game I made using Flash/AS3, to the Windows Phone using C#/XNA 4.0. You can see it here: http://goo.gl/gzFiE In the flash version I used a pixel-perfect collision between meteors (it's a rectangle, and usually rotated) that spawn outside the screen, and move towards the center, and a shield in the center of the screen(which is half of a semi-circle, also rotated by the player), which made the meteor bounce back in the opposite direction it came from, when they collided. My goal now is to make the meteors bounce in different angles, depending on the position it collides with the shield (much like Pong, hitting the borders causes a change in the ball's angle). So, these are the 3 options I thought of: Pixel-perfect collision (Microsoft has a sample) , but then I wouldn't know how to change the meteor angle after the collision 3 BoundingCircle's to represent the half semi-circle shield, but then I would have to somehow move them as I rotate the shield. Farseer Physics. I could make a shape composed of 3 lines, and use that as the collision object for the shield. Is there any other way besides those? Which would be the best way to do it(it's aimed towards mobile devices, so pixel-perfect is probably not a good choice)? Most of the time there's always a easier/better way than what we think of...

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• jBullet Collision/Physics not working as expected

  - by Kenneth Bray

  Below is the code for one of my objects in the game I am creating (yes although this is a cube, I am not making anything remotely like MineCraft), and my issue is I while the cube will display and is does follow the physics if the cube falls, it does not interact with any other objects in the game. If I was to have multiple cubes in screen at once they all just sit there, or shoot off in all directions never stopping. Anyway, I am new to jBullet, and any help would be appreciated. // Constructor public Cube(float pX, float pY, float pZ, float pSize) { posX = pX; posY = pY; posZ = pZ; size = pSize; rotX = 0; rotY = 0; rotZ = 0; // physics stuff fallMotionState = new DefaultMotionState(new Transform(new Matrix4f(new Quat4f(0, 0, 0, 1), new Vector3f(posX, posY, posZ), 1))); fallRigidBodyCI = new RigidBodyConstructionInfo(mass, fallMotionState, fallShape, fallInertia); fallRigidBody = new RigidBody(fallRigidBodyCI); }

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• 2D Collision in Canvas - Balls Overlapping When Velocity is High

  - by kushsolitary

  I am doing a simple experiment in canvas using Javascript in which some balls will be thrown on the screen with some initial velocity and then they will bounce on colliding with each other or with the walls. I managed to do the collision with walls perfectly but now the problem is with the collision with other balls. I am using the following code for it: //Check collision between two bodies function collides(b1, b2) { //Find the distance between their mid-points var dx = b1.x - b2.x, dy = b1.y - b2.y, dist = Math.round(Math.sqrt(dx*dx + dy*dy)); //Check if it is a collision if(dist <= (b1.r + b2.r)) { //Calculate the angles var angle = Math.atan2(dy, dx), sin = Math.sin(angle), cos = Math.cos(angle); //Calculate the old velocity components var v1x = b1.vx * cos, v2x = b2.vx * cos, v1y = b1.vy * sin, v2y = b2.vy * sin; //Calculate the new velocity components var vel1x = ((b1.m - b2.m) / (b1.m + b2.m)) * v1x + (2 * b2.m / (b1.m + b2.m)) * v2x, vel2x = (2 * b1.m / (b1.m + b2.m)) * v1x + ((b2.m - b1.m) / (b2.m + b1.m)) * v2x, vel1y = v1y, vel2y = v2y; //Set the new velocities b1.vx = vel1x; b2.vx = vel2x; b1.vy = vel1y; b2.vy = vel2y; } } You can see the experiment here. The problem is, some balls overlap each other and stick together while some of them rebound perfectly. I don't know what is causing this issue. Here's my balls object if that matters: function Ball() { //Random Positions this.x = 50 + Math.random() * W; this.y = 50 + Math.random() * H; //Random radii this.r = 15 + Math.random() * 30; this.m = this.r; //Random velocity components this.vx = 1 + Math.random() * 4; this.vy = 1 + Math.random() * 4; //Random shade of grey color this.c = Math.round(Math.random() * 200); this.draw = function() { ctx.beginPath(); ctx.fillStyle = "rgb(" + this.c + ", " + this.c + ", " + this.c + ")"; ctx.arc(this.x, this.y, this.r, 0, Math.PI*2, false); ctx.fill(); ctx.closePath(); } }

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